Ernst Lueder

Modeling of amorphous-silicon thin-film transistors for circuit simulations with SPICE

A static and dynamic model for amorphous silicon thin-film transistors is presented. The theory is based on an assumed exponential distribution of the deep states and the tail states in the energy gap. Expressions are derived that link the density of the localized states and the temperature to the drain current and the distribution of the charge in the transistor channel. In addition the authors take into account parasitic effects such as channel length modulation, off-resistance, drain and source resistances, mobile and free charges in the insulator, surface states, and overlap capacitances. The model is incorporated into the circuit simulation program SPICE. Charge conservation problems are overcome by using a charge-oriented dynamic transistor model. Simulated and measured current-voltage characteristics agree well. A 96-b gate line driver for addressing liquid-crystal displays, which was successfully designed and optimized with the model, is introduced. >

A surface micromachined capacitive absolute pressure sensor array on a glass substrate

Abstract The fabrication process and the characteristics of a new surface micromachined pressure sensor array on a glass substrate are presented. The array consists of electrically parallel individual sensors with composite SiO 2 -Cr-SiO 2 diaphragms and vacuum-sealed cavities underneath. The cavities are created by lateral etching of an Al sacrificial layer. Capacitive sensing of pressure is accomplished via chromic electrodes. The performance of the sensor array is described. In a pressure range of 800 kPa a terminal-based nonlinearity less than 4% was measured for the arrays. The pressure sensitivity of the array is about 0.28 fF hPa −1 .

Fourier optical realization of cellular neural networks

Cellular neural networks (CNNs) consist of analog, nonlinear, dynamic processing elements which are locally interconnected. Most applications in the areas of image processing, pattern recognition and robot control require interconnections between all elements which are space invariant. This suggests an optical CNN implementation because optical processors are perfectly suited for both space invariant signal processing and complete interconnections between all elements. The theoretical and practical aspects of a hardware realization are described. The results of an optical CNN performing feature extraction are presented. >

Matrix of light sensors addressed by a-Si:H TFTs on a flexible plastic substrate

A 2 inch matrix of 12288 light sensors was realized on a plastic substrate by low temperature thin film technology. In comparison to a glass realization the sensor matrix has a reduced weight, is unbreakable and flexible. Each sensor cell contains a photoconductor as a resistive sensor and a TFT for reading out the resistor values line by line. By using amorphous silicon for both the channel of the TFT and the photoconductor it is possible to fabricate the sensor matrix with a low number of masks. As gate insulator amorphous silicon nitride is used. The above mentioned films were deposited in a PECVD reactor in the same vacuum at 180 degree C which is suitable for PES-foils. The mismatch of the thermal expansion coefficients of the thin films and the plastic substrates causes peeling of the films and cracks. The remedy is the use of sputtered adhesion layers for the metallization and PECVD layers. To qualify the different adhesion layers a tape test method was used. Cracks were avoided by reducing the internal stress. For this reason a new layout was designed in which all PECVD layers are patterned in islands providing a minimum of internal stress. The TFTs show an ON/OFF ratio of 6 decades and a mobility of 0.3 cm2/Vs. The change of the a-Si:H conductivity under illumination is 6 nS/W/cm2. This value allows for a dynamic range of the sensor matrix of 60 dB. The new flexible sensor offers a wide variety of applications like an electronic eye with around view for the observation of wok pieces and traffic signs.

A flexible ferroelectric liquid-crystal display with improved mechanical stability for smart-card applications

— A bistable ferroelectric liquid-crystal display (FLCD) for application in a smart card has been developed together with Infineon Technologies Business Unit Security and Chip Card ICs. The manufacturing process of the display will be explained. To further improve the functionality and reliability of the display, its layout has been modified. Barrier layers to reduce water permeation have been introduced. Defects in the FLC have been observed around the spacers. A change in the process order can help to avoid them. To reduce the sensitivity of the smectic layers of the FLC to shear forces, a special display layout with enlarged spacers has been developed together with an appropriate vacuum-free filling process.

Generation of equivalent block parallel digital filters and algorithms by a linear transformation

A linear transformation of flow graph matrices of digital 2k-ports is introduced which leaves the transfer functions from each input to each output invariant thus generating equivalent 2k-ports. Examples for digital 2k-ports are block digital filters which, due to parallel processing, enhance the speed of operation or digital algorithms. An example for k = 2 demonstrates how the number of multipliers in a block digital filter can be reduced by 30%. A 3-point discrete Fourier transform (DFT) is transformed into its Winograd form.<<ETX>>

320‐dpi 4‐inch Reflective Stacked Crossed Guest‐Host Display

We describe a 320-dpi, 4-inch diagonal a-Si:H TFT-driven monochrome reflective display panel, in which two guest-host nematic liquid crystal layers separated by a thin polymer film are orthogonally aligned to realize high reflectivity and high contrast ratio simultaneously. The TFT manufacturer used a four mask process with a high aperture ratio. The structure and characteristics of the panel are presented.

Fast and accurate techniques for measuring the complex transmittance of liquid crystal light valves

A highly accurate measurement technique has been developed and applied for characterization of the complex transmittance of liquid crystal light valves (LC-LV). The measurement setup is based on a two-beam interference with partially coherent light. An arc lamp light source enables measurements over a large range of wavelengths. We propose a new Fourier transform interference pattern evaluation technique with a high signal-to-noise ratio. Calculations are sped up by FFT algorithms. Measurement results of the complex transmittance are shown for a twisted nematic and a Freederickzs liquid crystal light valve, built in our laboratory.

An array of TFT-addressed light sensors to detect grey shades and colours

An array of 12 288 pixels with light sensors in a-Si:H thin-film technology on a glass plate is described. An electronic circuit with a-Si:H-TFTs as switches in each pixel evaluates the grey shade of the light hitting the pixels. Colour filters allow detection of colours. The array of sensors is used to read video information such as drawings, pictures or documents with signatures without requiring optics. A lens in front of the array of cells enables it to detect distant objects.

Flexible and bistable FLC and cholesteric displays on plastic substrates for mobile applications and smart cards

Abstract— New smart-card applications like purse cards, etc. require an integrated display which allows the card-holder to read information which is stored on the IC of the card. On the other hand, the integration of a display into a plastic card requires some very specific features like flexibility and pressure stability, low-voltage CMOS-addressing, memory capability, and, of course, a reflective mode since no backlight is available. In this paper, two bistable reflective LCD solutions using ferroelectric and cholesteric LCs are discussed and very promising prototype results are presented. Pressure and bending tests as well as contrast measurements are compared in order to show the potential of meeting the requirements for use in smart cards.